Ink jet printing processes are of two types, continuous stream and drop-on-demand.
In continuous stream ink jet printing systems, ink is emitted in a continuous stream under pressure through a nozzle. The stream is perturbed, causing it to break up into droplets at a fixed distance from the nozzle. At the break-up point, the drop-lets are charged in accordance with digital data signals and passed through an electric static field which adjusts the trajectory of each droplet in order to direct it to a gutter for recirculation or to a specific location on a recording medium.
In the non-continuous process, or the so called "drop-on-demand" systems, a droplet is expelled from a nozzle to a position on a recording medium in accordance with digital data signals. A droplet is not formed and expelled unless it is to be placed on the recording medium.
The most important part of an ink for ink jet printing are the dyes. Although a number of dyes have been proposed none meets all the requirements of a modern printing process.
Reactive dyes with incorporated 1,3,5-triazine structural elements are common in textile printing. They have also been proposed as dyes for ink jet printing. For several reasons these dyes are not very suitable for this application. The reactive groups are not very stable over prolonged periods in aqueous solutions. Furthermore, dyes containing such reactive groups are due to their potential health risk, less suitable for handling in a non-chemical environment, where ink jet printing is normally done.
Dyes of different structures not containing reactive groups have been described for example in the patents U.S. Pat. No. 4,771,129, U.S. Pat. No. 4,780,532, U.S. Pat. No. 4,968,784, U.S. Pat. No. 4,975,118, U.S. Pat. No. 4,997,919 and U.S. Pat. No. 5,118,737 as well as in the patent applications JP 5-171,053, EP 0,187,520, EP 0,194,885 and EP 0,755,984 as being suitable dyes for inks for ink jet printing.
The azo dye of formula (1) ##STR2## has been described in patent application EP 0,187,520 (example 4). This dye and similar dyes described therein, however, are not soluble enough for their intended use in inks for modern ink jet printers.
The azo dye of formula (2) ##STR3## has been described in patent application EP 0,755,984 (dye 100). The very high water solubility of the azo dye of formula (2) and of similar dyes has been attributed to the introduction of the structural element (3) ##STR4## wherein R represents hydrogen or alkyl with 1 to 6 C atoms; M represents hydrogen, a metal cation or a substituted ammonium cation wherein the substituent is selected from the group consisting of alkyl, alkoxyalkyl or hydroxyalkyl each having from 1 to 12 C atoms; and n and m independently of each other have a value from 2 to 6.
Dyes having the structural element (3) mentioned above however show the disadvantage that they are not very stable against hydrolysis and that therefore inks containing such dyes are not stable when stored over long periods of time. They therefore do not satisfy all the required demands when used in recording liquids for ink jet printing.
Dyes used for such recording liquids have to show a good solubility in the essentially aqueous ink liquid, they have to penetrate into the recording medium and should not show dye aggregation on the surface of the recording medium ("bronzing"). They need to provide printed images having high optical density, good water fastness and excellent light fastness. They need to be stable in the ink even when the recording liquid is stored for a long time under adverse conditions. Various types of compositions have been proposed as inks for ink jet printing. Typical inks comprise one or more dyes, water, organic cosolvents and other additives.
The inks have to meet the following criteria:
(1) The ink gives high quality images on any type of recording medium. PA0 (2) The ink gives printed images exhibiting excellent water fastness. PA0 (3) The ink gives printed images exhibiting excellent light fastness. PA0 (4) The ink gives printed images exhibiting excellent smudge behavior. PA0 (5) The ink does not clog jetting nozzles even when these are kept uncapped while recording is suspended. PA0 (6) The ink can be stored for long periods of time without deterioration of its quality. PA0 (7) The values of the physical properties of the inks as viscosity, conductivity and surface tension are all within defined ranges. PA0 (8) The ink has to be non toxic, not flammable and safe. PA0 represents OR.sub.2 wherein R.sub.2 represents hydrogen or alkyl with 1 to 8 C atoms; PA0 m is from 2to 6; PA0 R.sub.1 represents hydrogen or alkyl with 1 to 6 C atoms; PA0 M represents hydrogen, a metal cation, ammonium or substituted ammonium, wherein the substituents are selected from the group consisting of alkyl, alkoxyalkyl or hydroxyalkyl each having from 1 to 12 C atoms or phenyl; guanidinium or substituted guanidinium, where the substituent is selected from the group consisting of alkyl with 1 to 12 C atoms or phenyl; PA0 F represents a monoazo or a polyazo dye radical. PA0 B represents one of the following groups ##STR7## wherein R.sub.5, R.sub.6 independently represent hydrogen, alkyl or alkoxy each having from 1 to 4 C atoms, chloro, bromo, carboxy or sulpho; PA0 D.sub.1 represents phenyl or phenyl substituted by one or two substituents selected from the group consisting of alkyl, alkoxy, chloro, bromo, carboxy and sulpho, or naphthyl or naphthyl substituted by 1 or 2 sulpho groups; PA0 p.sub.1 is 0 or 1; PA0 R.sub.7, R.sub.8 independently represent hydrogen, alkyl or alkoxy or acylamino with up to 3 C atoms; PA0 E represents phenyl or phenyl substituted by one or two substituents selected from the group consisting of alkyl, alkoxy, chloro, bromo, carboxy and sulpho, or naphthyl or naphthyl substituted by one or two substituents selected from the group consisting of sulpho, hydroxy and amino; PA0 D.sub.2 represents phenyl or phenyl substituted by one or two substituents selected from the group consisting of alkyl, alkoxy, chloro, bromo, carboxy and sulpho, or naphthyl or naphthyl substituted by one or two sulpho groups; PA0 p.sub.2 is 0 or 1; PA0 R.sub.9 represents hydrogen, alkyl with 1 to 6 C atoms, substituted alkyl with 2 to 6 C atoms, where the substituents are selected from the group consisting of carboxy, hydroxy and sulpho, phenyl or substituted phenyl, where the substituents are selected from the group consisting of methyl, chloro, bromo and sulpho; PA0 R.sub.10 represents CH.sub.3, COOH or NHCOCH.sub.3 ; PA0 R.sub.11, R.sub.12 independently represent hydrogen, chloro, bromo or methyl; PA0 R.sub.13 represents hydrogen, alkyl or alkoxy each having up to 3 C atoms; PA0 R.sub.14 represents alkyl with 1 to 8 C atoms, phenyl or phenyl substituted by one or more substituents selected from the group consisting of chloro, bromo, alkyl and alkoxy each having from 1 to 4 C atoms; PA0 p.sub.2 is 0 or 1; ##STR14## wherein M is as defined above; PA0 R.sub.15 represents hydrogen, alkyl or alkoxy each having up to 3 C atoms; PA0 R.sub.16 represents alkyl with 1 to 8 C atoms, substituted alkyl with 1 to 6 C atoms, where the substituents are selected from the group consisting of COOCH.sub.3, COOH and halogen, phenyl or phenyl substituted by one or more substituents selected from the group consisting of chloro, bromo, alkyl, alkoxy, alkylcarbonylamino and alkylsulphonyl each having from 1 to 4 C atoms, or pyridine; PA0 p.sub.3 is 0 or 1; PA0 R.sub.17, R.sub.18 independently represent hydrogen, chloro, bromo, ureido, alkyl, alkoxy or acylamino each having up to 3 C atoms; PA0 R.sub.19 represents hydrogen, alkyl or alkoxy with up to 3 C atoms; PA0 R.sub.20 represents hydrogen, alkyl with 1 to 6 C atoms, substituted alkyl with 2 to 6 C atoms, where the substituents are selected from the group consisting of CN, COOH, OH, COOCH.sub.3, COOCH.sub.2 CH.sub.3 and COCH.sub.3, phenyl or substituted phenyl, where the substituents are selected from the group consisting of methyl, chloro and bromo; PA0 R.sub.21, R.sub.22 independently represent hydrogen, chloro, bromo, ureido, alkyl, alkoxy or acylamino each having up to 3 C atoms; PA0 p.sub.4 is 1, 2 or 3 and the SO.sub.3 M group is in positions 1 or 4 or 5 or 6 or 7 or 8, when p.sub.4 is 1; or the SO.sub.3 M groups are in positions 4 and 8 or 5 and 7 or 6 and 8 or 1 and 5, when p.sub.4 is 2; or the SO.sub.3 M groups are in positions 3 and 6 and 8 or 4 and 6 and 8, when p.sub.4 is 3. PA0 (i) a compound of formula (5) ##STR20## wherein R.sub.1 and F are as defined above, is reacted with a compound of formula (6) ##STR21## wherein R.sub.3 and R.sub.4 are as defined above, under conditions that one of the chlorine atoms of the dichlorotriazine of formula (5) is replaced by the compound of formula (6); PA0 (ii) the disubstituted triazine is reacted with a compound of formula (9) ##STR24## wherein m is as defined above, under conditions that the third chlorine atom of the triazine ring is replaced by the compound of formula (9).